Johan Thorén | Searcharxiv

arXiv2018

QCD multiplet bases with arbitrary parton ordering

We develop an algorithm for recursively constructing orthogonal multiplet bases for the color space of QCD, for any order of partons and any Nc. This recipe is then applied for explicitly constructing some of these bases. Using the bases, a corresponding set of Wigner 6j coefficients are calculated. The Wigner coefficients offer a method of using multiplet bases without resorting to the explicit expressions of the basis vectors, which lead to a significant speed-up compared to other methods of treating full color structure.

hep-ph↗

arXiv2018

Color matrix element corrections for parton showers

We investigate the effects of keeping the full color structure for parton emissions in parton showers for both LEP and LHC. This is done within the Herwig 7 dipole shower, and includes gluon emission, gluon splitting, initial state branching processes, as well as hadronization. The subleading Nc terms are included as color matrix element corrections to the splitting kernels by evolving an amplitude-level density operator and correcting the radiation pattern for each parton multiplicity, up to a fixed number of full color emissions, after which a standard leading color shower takes over. Our results are compared to data for a wide range of LEP and LHC observables and show that the subleading Nc corrections tend to be small for most observables probing hard, perturbative dynamics, for both LEP and LHC. However, for some of these observables they exceed 10%. On soft physics we find signs of significantly larger effects.

hep-ph↗